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                [Sdoi2015]嫁接树                </h1>
                <p>时间限制：10s&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;  空间限制：512MB</p>			</div>
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                                <h3>题目描述</h3><p><div>Alice设计了一个树结构，有 N 个结点（包括根）被依次编号为 1 到 N ，由 N-1 条边连接。后来，Bob在上面增</div>
<div>加了 K 条原来没有的边（也就是说既不是自环，也不会因此产生重边）并称这样得到的图为&ldquo;K-嫁接树&rdquo;。现在A</div>
<div>lice希望对嫁接树的每一个结点进行染色，允许使用的颜色恰有 N 种，分别编号为 1 到 N 。Alice要求相邻两个</div>
<div>结点要涂上不同的颜色。假设颜色为 i 的结点有 ti 个，则Bob给出了如下的评价分数：</div>
<div><img src="../file/4089_0.png" width="401" height="86" alt="" /></div>
<div>其中 P 为非负系数。现在，Alice希望可以找到一种染色方案，使得Bob给出来的评分最大。你能帮助他吗？</div>
<div></div></p><hr/><h3>输入格式</h3><p><div>第一行有 2 个整数，依次为 N 和 K，如题所述。</div>
<div>第二行到第 N+K 行，每行有两个整数 u 和 v ，依次给出了 N+K-1 条边。</div>
<div>保证不存在自环，也不存在重边。</div>
<div>最后一行给定非负浮点数 P 。</div>
<div>K&le;2；1&le;N&le;20000；0&le;P&lt;10</div>
<div></div></p><hr/><h3>输出格式</h3><p><p>输出最大的可能评分，四舍五入保留到小数点后第三位。</p>
<div></div></p><hr/><h3>样例输入</h3><pre>9 0 
1 2 
1 3 
1 4 
1 5 
2 6 
2 7 
2 8 
2 9 
2.5</pre><hr/><h3>样例输出</h3><pre>0.253</pre><hr/><h3>提示</h3><p>没有写明提示</p><hr/><h3>题目来源</h3><p>没有写明来源</p>
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